Diamond and diamond-like substances have many properties, such as wear resistance, thermal, conductivity, acoustic transmission, and corrosion inertness, which make them desirable for a variety of industrial applications. To this end, diamond and diamond-like substances have been incorporated into tools of various purpose such as saw blades and drill bits. One method for incorporating diamond or diamond-like materials into a tool is known as chemical vapor deposition (CVD).
Various CVD techniques have been used in connection with depositing diamond or diamond-like materials onto a substrate. Typical CVD techniques use gas reactants to deposit the diamond or diamond-like material in a layer, or film. These gases generally include a small amount (i.e. less than about 5%) of a carbonaceous material, such as methane, diluted in hydrogen.
During the CVD process, the gases are heated to a temperature sufficient to separate the carbon atoms from the carbonaceous material, to which they are bound. Normally, such a separation would cause the carbon to be deposited on the substrate as amorphous carbon or graphite. However, when free carbon atoms are surrounded by hydrogen atoms, the carbon maintains an electron configuration of diamond (i.e. sp3 bonding) and deposits on the substrate as such. Further, even with the formation of non-diamond carbon on a substrate, a high hydrogen concentration readily converts the amorphous carbon or graphite back to methane. Thus, the concentration of hydrogen plays a key role in catalyzing the formation of diamond, and controlling the quality and purity thereof.
Various ways of heating the CVD gas mixture have been used, including hot filament, microwave agitation, oxyacetylene flame, and arc jet. While the temperature required for diamond deposition on a substrate is typically in the range of 800° C. to 900° C., the reaction temperature for the gases used is much higher. In fact, the higher the reaction temperature is, the more complete the decomposition of the gases into hydrogen and carbon atoms, and the faster the deposition rate of the diamond onto the substrate.
Of the above-recited heating methods, the hot filament method results in the slowest deposition rate (about 1 micron per hour), as it is only capable of reaching a temperature of about 2,200° C. in the filament. The microwave agitation method may achieve an intermediate deposition rate of about 10 microns per hour. The oxyacetylene flame method is capable of achieving a higher temperature than microwave agitation, and may yield a deposition rate of over 20 microns per hour. The arc jet method is capable of achieving the highest temperature (i.e. about 6,000° C.), and therefore yields the highest deposition rate, such as about 50 microns per hour.
It has been shown that higher deposition rates cause the diamond or diamond-like materials to be deposited over smaller areas of substrate surface. Thus, a higher rate of deposition may be more, or less, suitable for an application depending on the size of the device and the desired characteristics of the diamond or diamond-like portions thereof.
In forming a layer of diamond, or diamond-like material on a substrate using CVD techniques, a plurality of diamond grains, or “seeds,” may be first placed upon the substrate surface. The placement of such seeds may be accomplished using CVD itself. These seeds act as diamond nuclei and facilitate the growth of a diamond layer outwardly from the substrate as carbon vapor is deposited thereon. As a result, the growing side of the diamond layer becomes increasingly coarse in grain size, and must ultimately be ground and polished to a smooth finish such as by a mechanical means, in order to be suitable for many industrial applications. However, as diamond and diamond-like substances are among the hardest known materials, such mechanical grinding and polishing is difficult and tedious. Moreover, the cost of polishing often exceeds the cost for the diamond and film itself. In addition, mechanical polishing inevitably introduces micro-cracks or variations on the diamond surface. Such cracks and variations are detrimental to certain applications. For example, if the diamond is used make a surface acoustic wave (SAW) filter which is used to propagate surface acoustic waves, micro-cracks or variations in the diamond surface will introduce noise into the signal and therefore deteriorate the quality of the filtered wave.
Further, machine finishing is incapable of producing certain configurations in a diamond layer which are desirable or necessary for many industrial applications. For example, drilling a square hole through a diamond layer for creation of a wire drawing die that produces square shaped wires, is extremely difficult if not impossible.
In addition to the above-recited disadvantages, diamond or diamond-like materials which are produced by conventional CVD techniques are inefficient for making devices of certain purpose. Particularly, in many industrial applications, the surface of the diamond film requires a particular configuration in order to be of use. In such applications, the non-surface portion of the diamond or diamond-like material is unimportant to the performance of the device. However, conventional CVD techniques create the working surface by depositing thick films of diamond on the substrate and building up of the working surface to a body. Such a process wastes time and effort by slowly depositing a thick non-surface body of diamond or diamond-like materials.
As such, a process for making super-hard material containing devices which require little or no post synthesis work to achieve a finished product continues to be sought through on-going research and development efforts.